Process to prepare a lubricating base oil

ABSTRACT

Process to prepare two or more base oil grades, which base oil grades have different kinematic viscositys at 100° C. from a waxy paraffinic Fischer-Tropsch product having a content of non-cyclic iso-paraffins of more than 70 wt % by:
     (a) obtaining from the waxy paraffinic Fischer-Tropsch product a distillate fraction having a viscosity corresponding to one of the desired base oil products;   (b) performing a catalytic dewaxing step using the distillate fraction obtained in step (a) as feed;   (c) separating the lower boiling compounds from the dewaxed product obtained in step (b) in order to obtain the desired base oil; and   (d) repeating steps (a)–(c) for each base oil.

FIELD OF THE INVENTION

The invention is directed to a process to prepare a base oil from a waxyparaffinic Fischer-Tropsch product having a content of non-cycliciso-paraffins of more than 80 wt %.

BACKGROUND OF THE INVENTION

Such a process is known from EP-A-776959. This publication describes aprocess wherein the high boiling fraction of a Fischer-Tropsch synthesisproduct is first hydroisomerised in the presence of a silica/aluminasupported Pd/Pt catalyst. The isomerised product having a content ofnon-cyclic iso-paraffins of more than 80 wt % is subsequently subjectedto a pour point reducing step. The disclosed pour point reducing step inone of the examples is a catalytic dewaxing step performed in thepresence of a silica-supported dealuminated ZSM-23 catalyst at 310° C.

A disadvantage of such a process is that only one grade of base oils isprepared. A next disadvantage is that the hydrosiomerisation step isperformed on a narrow boiling range fraction of a Fischer-Tropschsynthesis product, which hydroisomersation step is especially directedto prepare a base oil precursor fraction having the desired properties.The hydroisomerisation process step can also yield valuable largevolumes of middle distillates next to base oil precursor fractions ifthe feed would also include more lower boiling compounds. There is thusa desire to prepare base oils from a waxy paraffinic fraction asobtainable from a hydro-isomerisation process step, which yields bothmiddle distillates, such as naphtha, kerosine and gas oil, and the waxyparaffinic fraction having a content of non-cyclic paraffins of morethan 80 wt %. There is also a desire to have a flexible process whereintwo or more base oils having different viscosity properties are obtainedof excellent quality.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a process wherein twoor more high quality base oils are prepared having different viscositiesfrom a waxy Fischer-Tropsch product.

Therefore, the invention is directed to a process to prepare two or morebase oil grades, which base oil grades have different kinematicviscosities at 100° C. than a waxy paraffinic Fischer-Tropsch producthaving a content of non-cyclic iso-paraffins of more than 70 wt % theprocess comprising

-   (a) obtaining from the waxy paraffinic Fischer-Tropsch product a    distillate fraction having a viscosity corresponding to one of the    desired base oil products,-   (b) performing a pour point reducing step using the distillate    fraction obtained in step (a) as feed,-   (c) optionally separating the lower boiling compounds from the    dewaxed product obtained in step (b) in order to obtain the desired    base oil, and-   (d) repeating steps (a)–(c) for each base oil.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a preferred embodiment of the process according the presentinvention

DETAILED DESCRIPTION OF THE INVENTION

Applicants found that by performing the process in the afore mentionedmanner a haze free base oil grade having also other excellent qualityproperties can be prepared. A further advantage is that in step (c) nohigher boiling compounds need to be removed. Thus an energy consumingdistillation step can be omitted. The advantages are even higher whentwo or more base oils are prepared having a difference in kinematicviscosity at 100° C. of less than 2 cSt.

The waxy paraffinic Fischer-Tropsch product having the high content ofnon-cyclic iso-paraffins of more than 70 wt %, preferably more than 80wt %, can be obtained by well-known processes, for example the so-calledcommercial Sasol process, the Shell Middle Distillate Process or by thenon-commercial Exxon process. These and other processes are for exampledescribed in more detail in EP-A-776959, EP-A-668342, U.S. Pat. No.4,943,672, U.S. Pat. No. 5,059,299, WO-A-9934917 and WO-A-9920720 all ofwhich are hereby incorporated by reference. The process will generallycomprise a Fischer-Tropsch synthesis and a hydro-isomerisation step asdescribed in these publications. The hydroisomerisation step is neededto obtain the required content of non-cyclic iso-paraffins in the feed.

In step (a) a distillate fraction having a viscosity corresponding toone of the desired base oil products is obtained from the waxyparaffinic Fischer-Tropsch product. Step (a) is suitably performed bymeans of distillation of a hydroisomerisation product. The distillationstep may include a first distillation at about atmospheric conditions,preferably at a pressure of between 1.2–2 bara, wherein lower boilingfractions, for example naphtha, kerosine and gas oil are separated froma higher boiling fraction. The higher boiling fraction, of whichsuitably at least 95 wt % boils above 350° C., preferably above 370° C.,is subsequently further separated in a vacuum distillation step whereina vacuum gas oil fraction, the distillate base oil precursor fractionand a higher boiling fraction are obtained. The vacuum distillation issuitably performed at a pressure of between 0.001 and 0.05 bara. Whenthe waxy paraffinic Fischer-Tropsch product is a high boiling mixture,having an initial boiling point of between 330 and 400° C., anatmospheric distillation step may suitably be omitted.

The distillate fraction, or the distillate base oil precursor fractionas obtained in step (a), has a viscosity corresponding to the desiredviscosity of the base oil product.

For targeted base oils having a kinematic viscosity at 100° C. ofbetween 4.5 and 6 cSt the kinematic viscosity at 100° C. of thedistillate fraction is preferably between 0.05 and 0.3 cSt lower thanthe target viscosity of the base oil. More preferably the kinematicviscosity at 100° C. of the distillate fraction as obtained in step (a)is between 0.8*P and 1.2*P, whereinP=vK@100p−ΔPP/200.In the above formula vK@100 p is the kinematic viscosity at 100° C. ofthe base oil product as to be obtained in step (c) expressed incentistokes and APP is the absolute difference in pour point of saidfraction obtained in step (a) and said product obtained in step (c) indegrees Celsius. Even more preferably said viscosity is between 0.9*Pand 1.1*P and most preferably about 1.

The kinematic viscosity at 100° C. of the distillate fraction ispreferably between 3 and 10 cSt. Suitable distillate fractions obtainedin step (a) have a T10 wt % boiling point of between 200 and 450° C. anda T90 wt % boiling point of between 300 and 650 more preferably between300 and 550° C.

In a preferred embodiment a first base oil grade having a kinematicviscosity at 100° C. of between 3.5 and 4.5 cSt and a second base oilgrade having a kinematic viscosity at 100° C. of between 4.5 and 5.5 cStare advantageously prepared in high yields by performing step (a) in afirst mode (v1) to obtain a base oil precursor fraction having akinematic viscosity at 100° C. corresponding to the first base oil gradeand in a second mode (v2) to obtain a base oil precursor fraction havinga kinematic viscosity at 100° C. corresponding to the second base oilgrade. By performing the pour point reducing step (b) separately on thefirst and second base oil precursor fractions high quality base oils canbe obtained.

In step (b) the distillate base oil precursor fraction obtained in step(a) is subjected to a pour point reducing treatment. With a pour pointreducing treatment is understood every process wherein the pour point ofthe base oil is reduced by more than 10° C., preferably more than 20°C., more preferably more than 25° C.

The pour point reducing treatment can be performed by means of aso-called solvent dewaxing process or by means of a catalytic dewaxingprocess. Solvent dewaxing is well known to those skilled in the art andinvolves admixture of one or more solvents and/or wax precipitatingagents with the base oil precursor fraction and cooling the mixture to atemperature in the range of from −10° C. to −40° C., preferably in therange of from −20° C. to −35° C., to separate the wax from the oil. Theoil containing the wax is usually filtered through a filter cloth whichcan be made of textile fibres, such as cotton; porous metal cloth; orcloth made of synthetic materials. Examples of solvents which may beemployed in the solvent dewaxing process are C₃–C₆ ketones (e.g. methylethyl ketone, methyl isobutyl ketone and mixtures thereof), C₆–C₁₀aromatic hydrocarbons (e.g. toluene), mixtures of ketones and aromatics(e.g. methyl ethyl ketone and toluene), autorefrigerative solvents suchas liquefied, normally gaseous C₂–C₄ hydrocarbons such as propane,propylene, butane, butylene and mixtures thereof. Mixtures of methylethyl ketone and toluene or methyl ethyl ketone and methyl isobutylketone are generally preferred. Examples of these and other suitablesolvent dewaxing processes are described in Lubricant Base Oil and WaxProcessing, Avilino Sequeira, Jr, Marcel Dekker Inc., New York, 1994,Chapter 7.

Preferably step (b) is performed by means of a catalytic dewaxingprocess. With such a process it has been found that base oils having apour point of below −40° C. can be prepared when starting from a baseoil precursor fraction as obtained in step (a) of the present process.

The catalytic dewaxing process can be performed by any process whereinin the presence of a catalyst and hydrogen the pour point of the baseoil precursor fraction is reduced as specified above. Suitable dewaxingcatalysts are heterogeneous catalysts comprising a molecular sieve andoptionally in combination with a metal having a hydrogenation function,such as the Group VIII metals. Molecular sieves, and more suitablyintermediate pore size zeolites, have shown a good catalytic ability toreduce the pour point of the distillate base oil precursor fractionunder catalytic dewaxing conditions. Preferably the intermediate poresize zeolites have a pore diameter of between 0.35 and 0.8 nm. Suitableintermediate pore size zeolites are ZSM-5, ZSM-12, ZSM-22, ZSM-23,SSZ-32, ZSM-35 and ZSM-48. Another preferred group of molecular sievesare the silica-aluminaphosphate (SAPO) materials of which SAPO-11 ismost preferred as for example described in U.S. Pat. No. 4,859,311hereby incorporated by reference. ZSM-5 may optionally be used in itsHZSM-5 form in the absence of any Group VIII metal. The other molecularsieves are preferably used in combination with an added Group VIIImetal. Suitable Group VIII metals are nickel, cobalt, platinum andpalladium. Examples of possible combinations are Ni/ZSM-5, Pt/ZSM-23,Pd/ZSM-23, Pt/ZSM-48 and Pt/SAPO-11. Further details and examples ofsuitable molecular sieves and dewaxing conditions are for exampledescribed in WO-A-9718278, U.S. Pat. No. 5,053,373, U.S. Pat. No.5,252,527 and U.S. Pat. No. 4,574,043 all of which are incorporated byreference.

The dewaxing catalyst suitably also comprises a binder. The binder canbe a synthetic or naturally occurring (inorganic) substance, for exampleclay, silica and/or metal oxides. Natural occurring clays are forexample of the montmorillonite and kaolin families. The binder ispreferably a porous binder material, for example a refractory oxide ofwhich examples are: alumina, silica-alumina, silica-magnesia,silica-zirconia, silica-thoria, silica-beryllia, silica-titania as wellas ternary compositions for example silica-alumina-thoria,silica-alumina-zirconia, silica-alumina-magnesia andsilica-magnesia-zirconia. More preferably a low acidity refractory oxidebinder material which is essentially free of alumina is used. Examplesof these binder materials are silica, zirconia, titanium dioxide,germanium dioxide, boria and mixtures of two or more of these of whichexamples are listed above. The most preferred binder is silica.

A preferred class of dewaxing catalysts comprise intermediate zeolitecrystallites as described above and a low acidity refractory oxidebinder material which is essentially free of alumina as described above,wherein the surface of the aluminosilicate zeolite crystallites has beenmodified by subjecting the aluminosilicate zeolite crystallites to asurface dealumination treatment. A preferred dealumination treatment isby contacting an extrudate of the binder and the zeolite with an aqueoussolution of a fluorosilicate salt as described in for example U.S. Pat.No. 5,157,191 or WO-A-0029511 both are hereby incorporated by reference.Examples of suitable dewaxing catalysts as described above are silicabound and dealuminated Pt/ZSM-5, silica bound and dealuminatedPt/ZSM-23, silica bound and dealuminated Pt/ZSM-12, silica bound anddealuminated Pt/ZSM-22 as for example described in WO-A-0029511 andEP-B-832171 both are hereby incorporated by reference.

Catalytic dewaxing conditions are known in the art and typically involveoperating temperatures in the range of from 200 to 500° C., suitablyfrom 250 to 400° C., hydrogen pressures in the range of from 10 to 200bar, preferably from 40 to 70 bar, weight hourly space velocities (WHSV)in the range of from 0.1 to 10 kg of oil per litre of catalyst per hour(kg/l/hr), suitably from 0.2 to 5 kg/l/hr, more suitably from 0.5 to 3kg/l/hr and hydrogen to oil ratios in the range of from 100 to 2,000litres of hydrogen per litre of oil. By varying the temperature between275 and suitably between 315 and 375° C. at between 40–70 bars, in thecatalytic dewaxing step it is possible to prepare base oils havingdifferent pour point specifications varying from suitably lower than −60to −10° C.

After performing a catalytic dewaxing step (b) lower boiling compoundsformed during catalytic dewaxing are removed in step (c), preferably bymeans of distillation, optionally in combination with an initialflashing step.

In step (d) steps (a)–(c) are repeated for every desired base oil.

In a preferred embodiment a first base oil (grade-4) is prepared havinga kinematic viscosity at 100° C. of between 3.5 and 4.5 cSt (accordingto ASTM D 445), a volatility of below 20 wt % and preferably below 14 wt% (according to CEC L40 T87) and a pour point of between −15 and −60° C.(according to ASTM D 97), more preferably between −25 and −60° C., bycatalytic dewaxing in step (b) a distillate fraction obtained in step(a) having a kinematic viscosity at 100° C. of between 3.2 and 4.4 cStand a second base oil (grade 5) is prepared having a kinematic viscosityat 100° C. of between 4.5 and 5.5, a volatility of below 14 wt % andpreferably below 10 wt % and a pour point of between −15 and −60° C.),more preferably between −25 and −60° C., by catalytic dewaxing in step(b) a distillate fraction obtained in step (a) having a kinematicviscosity at 100° C. of between 4.2 and 5.4 cSt.

FIG. 1 shows a preferred embodiment of the process according the presentinvention. In a process (1) a waxy paraffinic Fischer-Tropsch product(2) is prepared having a content of non-cyclic iso-paraffins of morethan 70 wt %. From this product (2) a distillate fraction (5) isobtained in distillation column (3) by separating of a light (4) andheavy fraction (6). This fraction (5) has a viscosity which correspondswith the desired base oil grade (10). In reactor (7) a catalyticdewaxing step is performed on the fraction (5) thereby obtaining adewaxed oil (8). By separating off light fraction (9) in distillationcolumn (11) the desired base oil grade (10) is obtained. By variation ofthe separation in distillation column (3) the properties of base oilgrade (10) can be varied according to the process of the presentinvention.

The above-described Base oil grade-4 can suitably find use as base oilfor an Automatic Transmission Fluids (ATF). If the desired kinematicviscosity at 100° C. (vK@100) of the ATF is between 3 and 3.5 cSt, theBase Oil grade-4 is suitably blended with a grade having a vK@100 ofabout 2 cSt. The base oil (grade-2) having a kinematic viscosity at 100°C. of about 2 to 3 cSt can suitably be obtained by catalytic dewaxing ofa suitable gas oil fraction as obtained in the atmospheric distillationin step (a) as described above. The Automatic Transmission Fluid willcomprise the base oil (blend) as described above, preferably having avK@100 of between 3 and 6 cSt, and one or more additives. Examples ofadditives are antiwear, antioxidant, and viscosity modifier additives.

The invention is furthermore directed to a novel class of base oilshaving a saturates content of above 95 wt %, preferably above 97 wt %, akinematic viscosity at 100° C. of between 8 and 12 cSt, preferably above8.5 cSt and a pour point of below −30° C. and a viscosity index of above120 preferably above 130. The combination of such low pour point highviscosity index fluids containing almost only cyclo, normal andiso-paraffins is considered-novel. Such base oils may be advantageouslyused as white oils in medicinal or food applications. To obtain a baseoil having the desired colour specification it may be required tohydrofinish the base oil, for example using a noble metal hydrofinishingcatalyst C-624 of Criterion Catalyst Company, or by contacting the baseoil with active carbon. Base oils having a colour according to ASTM D1500 of less than 0.5 and according to ASTM D 156 Saybolt of greaterthan +10 and even equal to +30 can thus be obtained.

The base oils obtained by the present process having intermediate vK@100values of between 2 and 9 cSt, of which preferred grade-4 and grade-5have been described above, are preferably used as base oil informulations such as gasoline engine oils, diesel engine oils,electrical oils or transformer oils and refrigerator oils. The use inelectrical and refrigerator oils is advantageous because of thenaturally low pour point when such a base oil, especially the gradeshaving a pour point of below −40° C., is used to blend such aformulation. This is advantageous because the highly iso-paraffinic baseoil has a naturally high resistance to oxidation compared to low pourpoint naphthenic type base oils. Especially the base oils having thevery low pour points, suitably lower than −40° C., have been found to bevery suitable for use in lubricant formulations such as gasoline anddiesel engine oils of the 0W–x specification according to the SAE J-300viscosity classification, wherein x is 20, 30, 40, 50 or 60. It has beenfound that these high tier lubricant formulations can be prepared withthe base oils obtainable by the process of the current invention. Othergasoline and diesel engine oil applications are the 5W–x and the 10W–xformulations, wherein the x is as above. The gasoline oil formulationwill suitably comprise the above-described base oil and one or more ofadditives. Examples of additive types which may form part of thecomposition are dispersants, detergents, viscosity modifying polymers,extreme pressure/antiwear additives, antioxidants, pour pointdepressants, emulsifiers, demulsifiers, corrosion inhibitors, rustinhibitors, antistaining additives, friction modifiers. Specificexamples of such additives are described in for example Kirk-OthmerEncyclopedia of Chemical Technology, third edition, volume 14, pages477–526.

The invention will be illustrated by the following non-limitingexamples.

EXAMPLE 1

1000 g per hour of a distillate fraction of an isomerisedFischer-Tropsch product having the properties as Feed N° 1 in Table 1was fed to a catalytic dewaxing reactor. The effluent of the catalyticdewaxing reactor was topped at 390° C. to remove only the light boilingfraction. The thus obtained base oil was recovered in a 69 wt % yieldbased on Feed N° 1. The dewaxing conditions are as in Table 2. Thecatalyst used in the dewaxing step was a Pt/silica bound ZSM-5 catalystas described in Example 9 of WO-A-0029511. The properties of the thusobtained base oils are in Table 3.

EXAMPLE 2

Example 1 was repeated except at different dewaxing conditions (seeTable 2). The properties of the base oil are in Table 3.

TABLE 1 Feed No. 1 2 Density at 70° C. 784.8 784.5 T10 wt % boilingpoint (° C.) 407 346 T90 wt % boiling point (° C.) 520 610 Kinematicviscosity at 5.151 6.244 10° C. (cSt) Pour point (° C.) +46 +30

TABLE 2 Dewaxing conditions Example 1 Example 2 Reactor temperature (°C.) 325 342 Hydrogen pressure (bar) 37 36 Weight hourly space 1.0 1.0velocity (kg/l/h) Hydrogen flow rate 700 700 (Nl/h)

TABLE 3 Example 1 Example 2 Feed Feed No. 1 Feed No. 1 Base oilproperties Density at 20° C. (kg/m³) 819.7 819.0 Kinematic viscosity at5.51 5.41 100° C. (cSt) Pour Point (° C.) −20 −48 Noack (wt %) 6.3 7.4

EXAMPLE 3

Example 1 was repeated at the conditions described in Table 4 using FeedNo. 2 (see Table 1). The properties of the resulting base oil arepresented in Table 5.

EXAMPLE 4

Example 1 was repeated at the conditions described in Table 4 using FeedNo. 2 (see Table 1). The properties of the resulting base oil arepresented in Table 5.

TABLE 4 Feed 2 Feed 2 Dewaxing conditions Example 3 Example 4 Reactortemperature (° C.) 290 296 Hydrogen pressure (bar) 48 47 Weight hourlyspace 1.0 1.0 velocity (kg/l/h) Hydrogen flow rate (Nl/h) 750 750

TABLE 5 Feed 2 Feed 2 Base oil properties Example 1 Example 2 Density at20° C. (kg/m³) 826 825.9 Kinematic viscosity at 100° C. 9.78 9.75 (cSt)Viscosity index 151 151 Pour Point (° C.) −9 −30 Noack (wt %) 6.1 6.0

The above experiments illustrate that base oils having a kinematicviscosity at 100° C. in the range of 3 to 12 cSt and especially 4 to 12cSt having excellent properties like pour point and viscosity index canbe obtained using the process according to the invention. It will beclear that by performing step (a) and (b) in a controlled manneraccording to the present invention all viscosity grades in that rangecan be sequentially obtained.

1. A process to prepare two or more base oil grades, which base oilgrades having different kinematic viscosities at 100° C. than a waxyparaffinic Fischer-Tropsch product having a content of non-cycliciso-paraffins of more than 70 wt %, the process comprising: (a)obtaining from the waxy paraffinic Fischer-Tropsch product a distillatefraction having a viscosity corresponding to one of the desired base oilgrades; (b) performing a catalytic dewaxing step using the distillatefraction obtained in step (a) as feed to produce a dewaxed productcomprising lower boiling compounds; (c) separating the lower boilingcompounds from the dewaxed product obtained in step(b) in order toobtain the base oil grade; and (d) repeating steps (a)–(c) for each baseoil grade, wherein the base oil having a kinematic viscosity at 100° C.of between 4.5 cSt and 6 cSt is prepared and wherein the kinematicviscosity at 100° C. of the distillate fraction as obtained in step (a)is between 0.8*P and 1.2*P, wherein P=vK@100 p−ΔPP/200, in whichequation vK@100 p is the kinematic viscosity at 100° C. of the base oilproduct as obtained in step (c) and ΔPP is the absolute difference inpour point of said fraction obtained in step (a) and said productobtained in step (c) in degrees Celsius.
 2. The process of claim 1,wherein the waxy paraffinic Fischer-Tropsch product has a content ofnon-cyclic iso-paraffins of more than 80 wt %.
 3. The process of claim1, wherein the kinematic viscosity at 100° C. of each of the differentbase oil grades differs from the kinematic viscosity at 100° C. of eachof the other base oil grades by less than 2 cSt.
 4. The process of claim1, wherein the distillate fraction has a T10 wt % boiling point ofbetween 200° C. and 450° C. and a T90 wt % boiling point of between 300°C. and 550° C.
 5. The process of claim 4, wherein the distillatefraction has a kinematic viscosity at 100° C. of between 3 cSt and 10cSt.
 6. The process of claim 1, wherein step (b) is performed by solventdewaxing.
 7. The process of claim 1, wherein step (b) is performed bycatalytic dewaxing.
 8. The process of claim 7, wherein the catalyticdewaxing is performed in the presence of a catalyst comprising a GroupVIII metal; an intermediate pore size zeolite having pore diameterbetween 0.35 nm and 0.8 nm; and, a low acidity refractory binder whichbinder is essentially free of alumina.
 9. The process of claim 1,wherein the kinematic viscosity at 100° C. of the distillate fraction asobtained in step (a) is between 0.9*P and 1.1*P.
 10. The process ofclaim 9, wherein the kinematic viscosity at 100° C. of the distillatefraction as obtained in step (a) is about equal to p.
 11. The process ofclaim 1, wherein a first base oil is prepared having a kinematicviscosity at 100° C. of between 3.5 cSt and 4.5 cSt, a volatility ofbelow 11 wt % and a pour point of between −15° C. and −60° C. bycatalytic dewaxing in step (b) a distillate fraction obtained in step(a) having a kinematic viscosity at 100° C. of between 3.2 cSt and 4.4cSt and a second base oil is prepared having a kinematic viscosity at100° C. of between 4.5 and 5.5, a volatility of below 14 wt % and a pourpoint of between −15° C. and −60° C. by catalytic dewaxing in step (b) adistillate fraction obtained in step (a) having a kinematic viscosity at100° C. of between 4.2 cSt and 5.4 cSt.